As illustrative of the prior art, reference can be made to the previous U.S. Pat. No. 4,023,229 dated May 17, 1977 in the name of Langdon Ross Blight and Alison Mary Blight.
This patent resulting in significant improvements in both the cost of manufacture of apparatus for washing out of plates and also in results obtainable in relation to the plates so washed out with the machine.
Significant problems still remain in relation to the overall design of such machines, especially when they are expected to handle plates of differing types, where for instance, the solvent material is extremely volatile, expensive, and toxic.
The machine previously described in my earlier Patent solved some of the problems, especially the danger of having electric switches and other dangers of electric sparking in close vicinity to the high vapour content, but there is the further problem that must be faced, namely that in the wash out of some plates, the cost of the solvent in itself becomes a very high operating expense simple because of the evaporation of this material aggravated by the nature of the mechanical action over the face of the material, and there is then the second problem that the vapours are generally considered toxic or in the very least, having effects on workers exposed to these fumes, the long term effects of which are simply not able to be forecast.
In other types of wash out apparatus, such as one in which the solvent is sprayed under high pressure jets at the plate, the problem is even more aggravated because of the high vapourization this spraying action will cause on the solvent.
There is a further problem in relation to present techniques for washing out these plates especially with this mechanical agitation, namely that the action must be such as to promote the removal of the unwanted material in a minimal time.
It must also achieve this with the highest degree of distinction between the unwanted and wanted material, so as not to in any way damage or unnecessarily remove some of the wanted material.
In other words, the mechanical action just cannot be that severe, and as will be seen from my previous Patent, the technique of mechanical agitation is very important but also a problem.
The problem comes from the difficulty of being able to ensure that any mechanical member for instance, a brush fibre is used in such a way and under such controlled pressure that even the finest projections on for instance, a printing plate, will not be inadvertently removed by undue pressure at any location on the plate.
The problem is to have such action uniform over a large plate area where the plate area may comprise separate segments which are separated by quite deep channels and which may have significantly higher or lower faces.
Furthermore, taking perhaps a brush face, having conventional bristles, differences in length of very small dimensions in relation to one bristle as compared to another are very difficult to achieve in practice, but unless almost negligible difference is achieved, where the brush is supported by a single fixed backing, then there will be significant differences in pressure applied over localized areas, and this will have a quite different result, area to area in the wash out action.
This will mean that some parts will become overwashed out or of course other parts can become under washed out in a given time, which results in printing plates perhaps of the photopolymer type which are not of good standard or perhaps more correctly put, of a standard that can preferably be reached.